1. Field of the Invention
The present invention relates to an image processing apparatus, an image reading apparatus, and an image processing system that restricts, when the image reading apparatus reads a copy-prohibited document, usage of the copy-prohibited document.
2. Description of the Related Art
There have been used multifunction peripherals (MFPs) having various functions such as a scanner that scans an original image, a copy machine that prints the original image obtained by the scanner, and a printer or a facsimile that prints image data received from an external device.
Some of the MFPs supports, for example, tool without an interesting name (TWAIN). In response to a command from an external device such as a personal computer (PC), the MFPs scan the image data, and process the obtained image data so that the external device can load the processed image data. Some of such MFPs transmit the obtained image data sequentially to the external device while scanning the image data because of limitation of a storage capacity, without storing the entire image data representing one page.
For example, if an original in A4 size is scanned at 600 dpi, a volume of the image data to be transmitted can be about 100 megabytes in an uncompressed state. In other words, the MFP that does not transmit the image data until the entire image data representing one page is stored is required to include a memory with a capacity of 100 MB or larger. However, such MFPs including a large-capacity memory will cost higher. To reduce the production cost by using a low-capacity memory, some of the MFPs transmit the obtained image data sequentially.
Moreover, if the MFP stores the entire image data representing one page and then transmits the stored image data, it takes longer time to transmit the entire image data, because the MFP cannot start data transmission until the entire image data is stored. Therefore, the MFP that sequentially transmits the stored image data while storing the obtained image data has an advantage in shortening the total transmission period.
There has been developed MFPs having a copy-prohibited document detecting function for determining whether the obtained image data represents a copy-prohibited document such as bills or securities. When the copy-prohibited document is detected, the MFPs delete or break the image data, or stop image-data transmission.
Japanese Patent Application Laid-open No. 2002-374409, for example, discloses a technology about a data transmitting apparatus that includes a data processing device including a storage unit and a filing device. When the data processing device determines that the image data represents the copy-prohibited document, the data transmitting device deletes the image data from the storage unit and transmits predetermined dummy image data instead of the image data to the filing device.
Japanese Patent Application Laid-open No. 2006-333015 discloses an image forming apparatus that processes, when it is determined that the image data represents the copy-prohibited document, the image data and notifies the user of a result of determination. With this configuration, it is possible to watch for image processing and prevent illegal image processing, without driving the user confused.
As described above, the data transmitting apparatus disclosed in Japanese Patent Application Laid-open No. 2002-374409 or the image forming apparatus disclosed in Japanese Patent Application Laid-open No. 2006-333015 deletes the image data stored therein, or transmits to the external device the dummy image data instead of the image data. In other words, if the obtained image data is transmitted sequentially to the external device, a part of the image data that the external device has received already remains unmasked, so that a malicious user can illegally obtain a part of the copy-prohibited image data.
The above problem arises because a certain volume of image data is required to detect the copy-prohibited document. For example, if the copy-prohibited document is detected by comparing a portion of the original with image patterns of parts of the copy-prohibited document, it is necessary to read a certain volume of image data enough for comparing the image pattern. In other words, the certain volume of image data has already been transmitted to the external device when the copy-prohibited document is detected using the above method.
Making use of this mechanism, the malicious user can forge the copy-prohibited document by, for example, combining parts of the image data that the external device has already received. It is difficult for the conventional technologies to prevent illegal usage of the image data.